The resting position of the Early Thorn distinguishes it from all other British thorns, with wings held back and close together, similar to a butterfly. The summer generation is smaller and paler, typically with larger tawny orange patches on the underside. Darker forms are encountered in the north.
The caterpillar can be found between May and June and again from August to early October in the south but in the north, where there is only one generation, caterpillars can be found between June and August. Overwinters as a pupa, spun between leaves or plant debris,